Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

SPLEEN

Figure 15.3. Massive splenomegaly secondary to myelofibrosis.

either one or two standard deviations from a group of “normal” spleens using the US splenic volume index.

Etiologies of splenomegaly are legion. Some radiologists subdivide splenomegaly into moderate versus massive, with the correspondingly most likely associated etiologies (Fig. 15.3). The most common causes of massive splenomegaly are myelofibrosis, lymphoma, and late-stage leukemia, although these entities are also encountered with lesser splenic enlargement. Splenomegaly is common in patients with portal hypertension. A rare cause of hepatosplenomegaly is systemic mastocytosis.

plasms, especially lymphoma, and noninfectious inflammatory conditions such as sarcoid (14).

Abscess

Splenic abscesses are not common. Most develop in a setting of systemic infection, trauma, diabetes, malignancy, or some hematologic disorder. Splenic flexure fistulas in colonic Crohn’s disease can involve the spleen and result in abscesses. Some left renal abscesses also involve the spleen. Likewise, a splenic abscess is a complication of a nephrectomy, especially if a nephrectomy is performed for xanthogranulomatous pyelonephritis. Common pathogens encountered are Staphylococcus and Streptococcus species and Escherichia coli. An occasional abscess contains Clostridium perfringens or other clostridial species.

Clinical signs and symptoms are nonspecific and include fever, pain, and left upper quadrant tenderness. Splenomegaly is usually present. Undiagnosed, splenic abscesses result in a high mortality rate.

Imaging should suggest the diagnosis (Fig. 15.4). In some patients a chest radiograph reveals a left pleural effusion. Most splenic abscesses are solitary. Computed tomography shows a hypodense region surrounded by

Infection/Inflammation

Most splenic infections are hematogenous in origin, although in some patients no primary focus of infection can be determined.

Small, focal, hypodense nodules scattered in the spleen on arterial phase CT images suggest an infection. A finding of such a “spotted spleen,” however, is also seen with some neo-

Figure 15.4. Splenic abscess detected by CT. It was of unknown etiology.

a contrast-enhancing rim. Gas within an abscess implies gas-forming bacteria; gas is only rarely secondary to an enteric fistula. A ruptured splenic abscess, however, has led to a pneumoperitoneum.

Most splenic abscesses have a slight heterogeneous MR appearance on precontrast images. Peripheral ring enhancement is common on postcontrast images.

Once imaging suggests a splenic abscess, culture of aspirated material should identify the infectious agent. Traditionally splenic abscesses have been treated by splenectomy, although they are amenable to percutaneous drainage, generally under US guidance, and percutaneous drainage has replaced splenectomy in a number of institutions.

Hydatid Disease

Hydatid disease is discussed in more detail in Chapter 7.Although most echinococcal cysts are located in either the liver or the lungs, an occasional cyst develops in the spleen, kidneys, bones, heart, or peritoneum. Usually splenic involvement is also associated with other disease, at times being recurrent. Rupture of a splenic echinococcal cyst results in peritoneal dissemination of cyst content.

Cyst wall calcifications develop in about half of splenic echinococcal cysts. Most have a welldemarcated outline; some are multiloculated

ADVANCED IMAGING OF THE ABDOMEN

(Fig. 15.5). Postcontrast CT reveals little contrast enhancement in the cyst wall.

Other splenic cysts, including the rare lymphangioma, are in the differential diagnosis.

Tuberculosis

Splenic tuberculosis is rare. Silent splenic involvement is found in some patients with disseminated tuberculosis. Typically multiple small, hypodense lesions are scattered throughout the spleen. No calcification is evident during an acute infection but develop with healing. The imaging appearance is nonspecific and is similar to that seen with a number of other infections and some lymphomas. Computed tomography revealed multiple, round or oval, hypodense tumors (Fig. 15.6). Ultrasonography of diffuse involvement reveals numerous hyperechoic foci. They are hypointense on T1weighted images and often heterogeneous on T2-weighted images. They do not enhance with contrast but tend to have a slight rim enhancement postcontrast. Splenic tuberculosis is often associated with extraperitoneal adenopathy, with the nodes having peripheral contrast enhancement.

The less common isolated tuberculoma mimics a splenic abscess.

Tuberculous splenic abscesses are photopenic with Tc-99m-sulfur colloid scintigraphy; these abscesses, however, have increased uptake during gallium-67 scintigraphy.

SPLEEN

Figure 15.6. Splenic tuberculosis in an HIV-positive man. Con- trast-enhanced CT shows marked splenomegaly and numerous poorly enhancing nodules throughout the spleen. Enlarged retroperitoneal nodes were also identified. (Courtesy of Patrick Fultz, M.D., University of Rochester.)

Candidiasis

A Candida sp. splenic abscess in the absence of immunocompromise is rare. Both preand postcontrast CT aid in detecting these multiple, often small abscesses. They tend to be hypodense. A typical US appearance is that of a bull’s-eye, a finding that is neither specific nor always seen. These abscesses appear hypointense on T1and hyperintense on T2weighted images. They do not enhance postcontrast.

If large enough, these abscesses are amenable to percutaneous drainage.

Histoplasmosis

Multiple small, punctate intrasplenic calcifications develop in patients with past histoplasmosis infection. Tuberculosis shows similar findings. In both entities calcifications are indicative of inactive disease.

Imaging readily detects these granulomas.

Brucellosis

Human brucellosis is caused by Brucella abortus, B. suis, B. canis, and B. melitensis. The latter is considered to be the most virulent.

Among patients with brucellosis from Beirut, Lebanon, the main presenting symptoms were

fever, sweating, fatigue, and joint pain, with osteoarthritic involvement being the most prevalent complication (15). Abdominal complaints were not common.

Calcifications in splenic brucellosis have an irregular and mottled appearance. Of interest is that with most infections calcifications imply disease inactivity within that nidus; brucellosis is unique in that active infection can be present even in a calcified nidus.

Cat-Scratch Disease

(Bartonella Infection)

Bartonella henselae infection is related to contact with cats and is the presumed cause of cat-scratch disease. If disseminated, this infection leads to focal multinodular liver and splenic granulomas.

The splenic granulomas eventually calcify, often having a coarse appearance.

Infectious Mononucleosis

(Epstein-Barr Virus Infection)

While splenomegaly is common in patients with infectious mononucleosis, in the occasional patient with disproportionate splenomegaly an underlying hematologic malignancy or a storage disorder such as Gaucher’s disease should be considered.

Some physicians believe that early splenectomy is indicated in a setting of splenic rupture complicating infectious mononucleosis, and most patients with spontaneous splenic rupture undergo splenectomy, although a nonoperative approach is feasible in selected patients. Even with initial nonoperative management, some eventually require a splenectomy.

Metabolic and Related

Disorders

Hypersplenism

Hypersplenism, or increased splenic hemolysis, is a manifestation of several disorders, such as thrombocytopenic purpura and Gaucher’s disease. Transcatheter splenic artery embolization is effective therapy for hypersplenism.

Platelets, white blood count, and liver function tests improve significantly after such embolization. Fever, abdominal pain, pleural effusion, and ascites are transient phenomena after splenic embolization.

Partial splenic embolization can be therapeutic in cirrhotic patients with hypersplenism. Residual spleen volumes remain stable in those with infarction rates >80%; on the other hand, in patients with lower infarction rates spleen volume tends to increase. The ideal splenic volume to be embolized is not clear and probably varies depending on disease and age. For instance, children with hypersplenism undergoing 30% to 40% splenic volume embolization have lower morbidity compared with those undergoing more extensive splenic embolization (16); all maintained a platelet count above baseline.

ADVANCED IMAGING OF THE ABDOMEN

Amyloidosis

Splenic involvement occurs in both primary and secondary amyloidosis. Diffuse rather than focal splenic involvement is more common. Abnormal regions tend to be hypodense on CT. Some foci calcify. Arterial phase CT in a patient with primary liver and spleen amyloidosis revealed lack of contrast enhancement (17); the spleen was hypointense on T2-weighted MR images.

Systemic amyloidosis is associated with hyposplenism. Among patients with suspected liver amyloidosis, a liver-spleen scan is quite sensitive in detecting decreased splenic activity and can suggest disease even before abnormal red blood cells are detected in a peripheral smear.

An amyloid spleen predisposes to a spontaneous splenic rupture.

Hyposplenism

The classic example of decreased splenic function is in sickle cell disease. For unknown reasons patients with celiac disease also develop hyposplenism. Decreased splenic function is detected by the presence of abnormal red blood cells and by finding decreased splenic uptake on a Tc-99m–sulfur colloid scan.

Hyposplenism increases the risk of infection and predisposes to spontaneous splenic rupture.

Extramedullary Hematopoiesis

Extramedullary hematopoiesis is most common in patients with congenital hemolytic anemias. Most foci occur in the liver and spleen but are too small to identify with imaging. If large enough, CT reveals a homogeneous hypodense tumor, suggesting an infection or neoplasm.

Iron Overload

Similar to the liver, MRI of the spleen detects relatively low levels of splenic iron overload, but for meaningful results stringent equipment calibration is necessary. Iron overload is difficult to quantify but is occasionally useful in adults with suspected posttransfusion iron overload. In children after autologous bone marrow transplantation, MRI detects earlier iron overload in the liver than in the spleen.

Sarcoidosis

Splenic abnormalities are present in roughly half of patients with sarcoidosis, with splenic involvement usually being asymptomatic and overshadowed by other organ involvement. The most common abdominal manifestation of sarcoidosis is hepatosplenomegaly, although marked splenic enlargement is rare. Less often seen are splenic nodules (18), an appearance called spotted spleen. Usually these splenic nodules are larger than their counterparts in the liver. They are not specific to sarcoidosis and are also found with some malignancies and infections. Punctate calcifications develop in some sarcoid spleens; these calcifications are readily identified by imaging and are similar to those seen with histoplasmosis and tuberculosis. Chest radiography is normal in some patients with splenic sarcoidosis.

Computed tomography reveals sarcoid nodules to be hypodense to splenic parenchyma and hypointense on MRI; they are best identified on T2-weighted fat-suppressed images and on immediate contrast-enhanced images. Ultrasonography reveals solid, hypoechoic foci.

Extraperitoneal adenopathy is common. Computed tomography also often detects an increased number of normal-sized lymph nodes.

SPLEEN

Virus-Associated Hemophagocytic

Syndrome

Virus-associated hemophagocytic syndrome consists of erythrocyte and other blood element phagocytosis in multiple organs, including the spleen. Magnetic resonance imaging in a patient with acute lymphocytic leukemia and virus-associated hemophagocytic syndrome revealed multiple, round splenic signal voids believed to represent hemosiderin deposits (19).

Tumors

Nonneoplastic

Inflammatory Tumor

The term inflammatory tumor, also called inflammatory pseudotumor and inflammatory myofibroblastic tumor, describes a focal inflammatory and reactive response in the spleen. The etiology of these rare tumors is unknown. They consist of a discrete encapsulated tumor containing a mixture of spindle cells suggesting myofibroblasts, inflammation, fibrosis, and necrosis.

They vary considerably in size and number. Some are quite large. They contain a mix of solid and cystic components. Computed tomography reveals a heterogeneous tumor. A central scar is suggested in some. They enhance less than normal spleen on early phase CT, but delayed enhancement is evident on later phases. They are heterogeneous and hypoto isointense to splenic parenchyma on T1and hypoto hyperintense on T2-weighted MR images. Similar to CT, delayed enhancement is evident postgadolinium. Their overall appearance is nonspecific and a preoperative diagnosis is difficult; the differential includes a malignancy.

A number of patients with an eventually diagnosed splenic inflammatory tumor have undergone a splenectomy.

Hemangioma

Some authors classify splenic hemangiomas under neoplasms, together with angiomas

and angiosarcomas. Although imaging findings overlap somewhat for these entities, pathogenetically hemangiomas are generally considered to be development anomalies and probably should be classified under hamartomas, but they have a sufficiently unique imaging appearance that they are discussed separately; keep in mind that an occasional splenic hemangioma exhibits sarcomatoid changes.

Splenic hemangiomas range from single to multiple. Multiple hemangiomas occur in the Klippel-Trénaunay-Weber syndrome. Hemangioma complications include hemorrhage and rupture. One infant with splenic hemangiomatosis had life-threatening thrombocytopenia, anemia and intravascular coagulopathy (Kasabach-Merritt syndrome) (20); whether these tumors indeed represented hemangiomatosis or a hemangioendothelioma is not clear.

Similar to liver hemangiomas, CT shows a low-density tumor with a peripheral hypervascular contrast-enhancing rim. Unlike in the liver, however, splenic hemangiomas less often show progressive central enhancement (Fig. 15.7).

Gray-scale US reveals hemangiomas as wellmarginated, homogeneous and hyperechoic tumors (Fig. 15.8).

Figure 15.7. Presumed splenic hemangioma. Early contrastenhanced CT image reveals a hypodense tumor. Delayed views showed that this tumor fills in from the periphery and becomes nearly isodense with the spleen. A similar tumor was present on CT images 19 months previously. (Courtesy of Patrick Fultz, M.D., University of Rochester.)